Heterogeneous reaction of HOI with sodium halide salts

The interaction of gaseous HOI with crystalline grains of NaCl and sea-salt and thin films of NaBr crystals has been studied in a walt coated tubular flow reactor coupled to a quadrupole mass spectrometer over a concentration range (0.2-8) x 10(12) molecules cm(-3) at 278 and 298 K. On a fresh surfa ce, the uptake coefficients determined were independent of temperature with gamma = 0.034 +/- 0.009, gamma = 0.016 +/- 0.004, and gamma = 0.061 +/- 0. 021 for NaBr, NaCl, and sea-salt, respectively. No increase in reactivity w as observed on addition of water vapor between 0 and 23% relative humidity at 278 K, It was also shown that the reactivity of the salt surface decreas ed with time of exposure to HOI and that steady-state uptake was slower on "aged" salt surfaces. Products of the reactions released into the gas phase were IBr, ICI, and IBr + ICI for the reaction of HOI on NaBr, NaCl, and se a-salt surfaces, respectively. The atmospheric implications of the results obtained are briefly discussed.